Standard visit visa queries

[ahmad101112]

Hi,
I am applying for a visit visa for my mother to join me (pbs dependant) and my husband British citizen for helping me around my pregnancy.I am sponsoring the trip.

I have few difficulties in filling the form
There are few questions in the form:-

1-how much money are you planning to spend in the U.K.?
I tried £0 (as we are sponsoring ) but the form doesn’t accept it.
2-How much money do u spend every month?

Also,it would be of immense help if I get a checklist of all the supporting documents
I’ll need to send to her before her vfs appointment .
Thanks.